Glass fiber mat for reinforcing plastics has been made for many years in two principle forms, one being chopped strand mat, and the other being swirl continuous strand mat. In both mats, the fiber of the strands are held together by a size and the strands are in turn bonded together by a small amount of organic binder which softens or sometimes dissolves to some degree in later applied organic impregnating resin; so that the strands become unbonded to allow the mat to stretch over projections during the molding or during the hand lay up process. It turns out that the maximum amount of randomly oriented strand that can be impregnated with resin or a molding compound is about 25% by volume. Glass fibers are very strong and they provide a major portion of the strength of the finished molded product. The prior art has long known that if the fibers could be laid parallely that the strength of the finished product, at least in one direction, would be greatly increased. This fact has been made use of in the filament winding process, wherein the strands are tightly wound onto a mandrel while they are wetted with a liquid resin to give products wherein the glass fibers may comprise 50% by volume or more of the finished product. The process produces generally cylindrical envelopes having great hoop strength, as is necessary in pipes and tanks. Additionally, circumferentially extending strips have been cut from the envelopes for automotive bumpers and the like.
An object of the present invention is the provision of a new and improved mat which will give a fiber loading of greater than 25% by volume and which can be stretched or bent during the molding, or part forming operation without having the mat "thin out" detrimentally when pulled over projections of a mold.
Another object of the present invention is the provision of a new and improved mat which will provide molded parts having greater strength in predetermined directions at predetermined fiber loadings than has been possible with prior art mats.
Another object of the present invention is the provision of a new and improved mat having parallely oriented fibers which do not separate during molding over projections.
A further object of the present invention is the provision of a new and improved sheet molding compound having a mat therein with generally parallely oriented fibers and which can be molded into complicated shapes without separation of the parallely oriented fibers.
Further objects and advantages of the present invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments.